This invention relates to a process for coprecipitating malachite with bismuth, to a process of making a cuprous acetylide complex ethynylation catalyst starting with such coprecipitation, and to the complex produced.
In the production of 1,4-butynediol by the reaction of acetylene with formaldehyde in the presence of a cuprous acetylide complex catalyst, it is known to be desirable to inhibit the formation of cuprene, polymerized acetylene, by the use of inhibitors such as bismuth oxide. U.S. Pat. No. 2,300,969 -- Reppe et al. (1942) discusses the use of several such inhibitors in the formation and use of such catalysts at elevated pressures such as about 20 atmospheres. U.S. Pat. No. 3,650,985 -- Kirchner (1972) mentions the utility of bismuth oxide as a cuprene inhibitor in cuprous acetylide catalyst made and used at low partial pressures of acetylene, below 2 atmospheres. Neither of these patents indicates how the bismuth values can be incorporated uniformly into the catalyst itself.
It has been found that in the production of the low pressure catalysts according to U.S. Pat. No. 3,650,985, if bismuth oxycarbonate is added separately to preformed malachite, it will separate in the catalyst which is eventually prepared, leading to unsatisfactory results. Thus, it is desirable to have a satisfactory method of coprecipitating bismuth in the basic cupric carbonate or malachite which is the catalyst precursor.
Basic copper carbonate, known as malachite, Cu.sub.2 (OH).sub.2 CO.sub.3, is normally prepared by either of two precipitation techniques. In the first, a solution of a copper salt such as copper nitrate or chloride is neutralized to a pH of 7.0 with sodium or potassium carbonate or bicarbonate. Initially, hydrated copper carbonate, amorphous CuCO.sub.3.x(H.sub.2 O), precipitates in the form of a thick gelatinous material which, on heating, slowly converts to malachite with the elimination of CO.sub.2. Precipitates of crystals of malachite made by this technique generally comprise irregularly shaped particles ranging in size from less than 1 micron (.mu.) to more than 25 .mu. in average particle cross-sectional dimension. If the gel has set up thoroughly, then the irregularity and broad distribution of crystallite size on crystallization seem to be a result of tearing of the gel as it precipitates. The irregularly-shaped crystallites and wide distribution of particle size is rather undesirable for use as a precursor in the production of cuprous acetylide ethynylation catalysts.
Another method for the precipitation of malachite involves feeding simultaneously the copper solution and the carbonate neutralization agent with agitation to maintain a pH in the range of 5 to 8. The hydrated copper carbonate so obtained is also subsequently converted to malachite at ambient temperature or more rapidly as the temperature is increased. This technique produces a more regular crystalline product which consists of agglomerates of individual crystallites of about 2 to 3 .mu. average cross-sectional dimension. The agglomerates range in size up to a maximum of about 30 .mu.. As with the first method of adding the carbonate neutralizer to the copper solution, so too with this method of simultaneously feeding them together, an amorphous hydrated copper carbonate is initially formed.
It would be desirable to have a process for the production of basic copper carbonate crystalline particles having bismuth incorporated therein with the particles being of a fairly uniform and relatively large particle size. The uniformity of dispersion of bismuth in the particles is desirable to permit the formation of ethynylation catalyst in which the bismuth values will remain in place and continue to be effective in the prevention of cuprene formation.